The power adapter replaces the position of linear power supply with the advantages of high efficiency, low power consumption, small volume, portability, light weight, convenient carrying, strong anti-interference and wide output voltage range The power adapter is mainly composed of control circuit, input rectifier filter, integrated circuit, power switch tube, protection circuit, output rectifier filter, switching power transformer, input power grid filter and so on
1. Control circuit: detect the output DC voltage, compare it with the reference voltage, amplify and modulate the pulse width of the oscillator, so as to control the converter to maintain the stability of the output voltage The output voltage adjustment rate of general power adapter is 5%
2. Input rectifier filter: the 220V or 110V AC voltage input from the power grid is rectified and filtered to provide DC voltage for the converter For example, the function of rectifier bridge is to change AC into DC, while the function of filter capacitor is to filter the AC ripple in DC and make the circuit work more reliably
3. Integrated circuit (operational amplifier IC), protection circuit and voltage regulation are important components
4. Power switch tube: the power switch tube is one of the core components in the switching power supply. The switch tube works alternately in the positive feedback and negative feedback circuits. The positive feedback is responsible for conduction and the negative feedback is responsible for cut-off
5. Protection circuit: in case of over-current, over-voltage, over-power and short circuit, the protection circuit stops the power adapter to protect the appliance and the power adapter from damage For example, protect the varistor in the current. The principle of varistor is that when the external voltage is too high, the resistance of varistor quickly becomes very small. At this time, the resistance of varistor decreases and the current is shunted to prevent damage or interference by excessive instantaneous voltage, so as to protect other circuits from damage
6. Output rectifying filter: rectifying and filtering the high-frequency AC voltage output by the converter to obtain the required DC voltage, while preventing the interference of high-frequency noise to the load Such as filter capacitor, it can filter out the ripple in low voltage DC
7. Switching power transformer: switching power transformer is a power transformer with switch tube. In addition to the voltage conversion function of ordinary transformer, it also has the functions of insulation isolation and power transmission. It is generally used in fields involving high-frequency circuits such as switching power supply
8. Input power grid filter: eliminate the interference from the power grid, such as motor startup, electrical switch, lightning strike, etc., and prevent the diffusion of high-frequency noise generated by switching power supply to the power grid Such as inductance coil (also known as choke), the main function is to reduce electromagnetic interference
